Electrodeposition of bright tin



United States Patent Ofiice 3,361,652 Patented Jan. 2, 1968 3,361,652 ELECTRODEPOSITION OF BRIGHT TIN Joachim Korpiun, Friedrich Sedlacek, and Joachim Steeg,

Geislingen an der Steige, Germany, assignors to Dr. Ing. Max Schlotter, Geislingen an der Steige, Germany, a

firm No Drawing. Filed Aug. 24, 1964, Ser. No. 391,790 Claims priority, application Germany, Aug. 28, 1963, Sch 33,772; Aug. 5, 1964, Sch 35,588 16 Claims. (Cl. 204-54) ABSTRACT OF THE DISCLOSURE Semi-bright or bright tin electrodeposits are formed in otherwise conventional acid tin baths in the presence of a dissolved primary brightener of the formula in which X is phenyl, furfuryl, or pyridyl and Y may be hydrogen, formyl, carboxyl, alkyl, hydroxyalkyl, formylalkyl, or the acyl radical of a carboxylic acid. Formaldehyde and certain imidazoline derivatives act as secondary brighteners, particularly when employed with nonionic wetting agents.

This invention relates to a method of electrodepositing bright tin, and to an acid solution suitable as an aqueous electrolyte for performing the method.

Commercially used bright acid tin plating solutions contain as brighteners tar and tar fractions obtained in the destructive distillation of wood. Such electrolytes are difficult to control, and it is not readily possible to produce :bright tin plates of consistent quality from them over extended periods of time.

We have found a group of primary brighteners for acid tin plating electrolytes which perform reliably over extended periods of operation, and yield semi-bright or fully bright deposits in a reproducible manner. The primary brighteners of the invention cooperate with secondary brighteners which improve brightness and/ or widen the cathode current density range in'which the deposits have the desired brightness.

Wetting agents are employed in the acid tin plating solutions of the invention. Non-ionic wetting agents are preferred, and the water soluble ether of polyglycols which are readily available are both effective and stable under the normal operating conditions of the electrolyte. They may have from ten to thirty ethyleneoxy radicals per molecule, the molecular weight being mainly limited by considerations of solubility.

The primary brighteners of the invention are soluble ethylene derivatives of the formula XCH=CHY wherein X is phenyl, furfuryl or pyridyl, and Y may be hydrogen, formyl, carboxyl, alkyl, hydroxyalkyl, formylalkyl, or the acyl radical of a carboxylic acid, the nature of the substituents being limited mainly by the requirement that the brightener be soluble in the electrolyte in effective amounts.

The following examples are representative of compounds which are adequately soluble in the acid electrolytes of the invention:

3-furylacrylic acid-C H OCH=CHCOOH BenzylideneacetoneC H CH=CHCOCH Cu rcumin [C H (OH) (OCH )-CH=CHCO] :CH 4-(2 furyl)-3-butene-2-one- C H O-CH=CHCOCH 4-p-sulfophenyl-3-butene-2-one- C H (SO H)CH=CHCOCH 1,S-di-p-sulfophenyl-I,4-pentadiene-3-one- 2-pentyl-3-phenyl-propenal-- C H CH=CH( CH CHO 4-hydroxy-3-methoxy-benzylideneacetone C H (OH) (OCH )-CH=CHCOCH 4-(pyridyl-2)-3-butene-2-one C H NCH=CHCOCH As is evident from the examples listed above, the length of carbon chains attached to the ethylene core of the brightening agent does not interfere with the brightening effect as long as adequate solubility is maintained, nor are substituents in the radicals X and Y of importance as long as they do not affect the stability of the brightener in a harmful manner.

The primary brighteners are listed in part in the Merck Index, 7th ed., with their methods of preparation. The compounds not listed in the Index may be prepared according to the following publications:

o-Methoxycinnamic acid: J. Chem. 414 (Perkin);

4-(2-furyl)-3-butene-2-one; Ber. 14, 1459 (Schmidt);

4-phenyl-3-butene-2-one-1-sulfonic acid and 1,5-diphenyl-1,4-pentadiene-4-one-2,4-disulfonic acid: Zentralblatt 1954, p. 1927;

Z-pentyl 3 phenyl propenal: (1953) 1012 (Durr);

4-hydroxy-3 -methoxy-benzylideneacetone: Soc. (London) 1938, p. 1568 (Nisbet); and

4-(pyridyl-2)-3-butene-2-one: Zentralblass, 1962, page 728.

Soc. (London) 31,

Comptes Rendus 237 J. Chem.

The concentrations of tin and free acid may be varied generally within the limits conventional in this art. A tin content of 10 to grams per liter, and a free acid concentration of 20 to 200 grams per liter are typical of the sulfate, fluoborate, and aromatic sulfonate solutions, known in themselves, which may be provided with the brighteners of the invention. Sulfuric, fluoboric, and aromatic sulfonic acids may be present simultaneously in the electrolytes in a manner not novel in itself.

The secondary brighteners, which are employed in conjunction with the olefinic primary brighteners in the tin plating solutions of the invention include formaldehyde and certain imidazoline derivatives which may be employed singly or in combination with each other. The imidazoline derivatives Which have been found to Widen the bright and semi-bright current density range are of the formula R is hydrogen or the radical CH COOH, and R is hydrogen or a monovalent metal, particularly an alkali 3 metal. It will be appreciated that the metal may be replaced by hydrogen in the acid electrolyte, and other brighteners of the invention containing carboxyl groups or sulfo radicals may thus be incorporated in the electro- (III) Furfurylideneacetone or 4-(2-furyl)-3-butene- 2-one o-Methoxycinnamic acid 2-furylacrylic acid lyte in the form of their salts. 5 (VI) Benzylideneacetone Although the imidazoline derivatives described herein- (VII) 2-pentyl-3-phenylpropenal above are surface active because of the presence of rela- (VIII) Pyridylideneacetone or 4-(pyridyl-2)-3-butenetively long alkyl chains together with hydrophilic groups, 2-one it is peeferred employ them R F i 9 The plating solution I was originally somewhat turbid, non-1on1c wetting agents. The imidazollne derlvatlves, 10 but became clear after about one however, may replace a portion or all of the formaldehyde which would otherwise be necessary for producing a de- Example 2 Sirfid brightening f Similar results were obtained with fluoborate bath of The amounts of pnmary and secondary bnghteners to the following composition; be employed vary greatly according to the nature of the Grams/liter substituents present 1n the primary brlghtener, and such Tin (as fl b t 45 process variables as the configuration of the ob ect which Fluoboric acid 90 1s made the cathode during the platlng process, the de- Ether f polyglycol 2 sired rate of depositions, and the like. Guidance for the Formalin 1 use of the bnghteners will be found herelnbelow 1n the cinnamaldehyde 0 5 specific examples of embodnnents of th1s invention. Among the secondary brighteners, the imidazole deriva- The ether of p y lf employed contamed PP Q tives are effective in concentrations as low as 0.01 gram mately CZHLO {adlcals Per molecule" The esolunon per liter, and their beneficial effects increase with concengave bnghtest deposits at We between 20 and tration up to approximately 0.05 to 2.0 grams per liter, the and atPathOde current densmes of 1 to 4 amps limit varying from compound to compound At higher per square decimeter. When the c1nnamaldehyde Was reconcentrations, no further significant improvement is ob- Placed the 9 301mm? by gram/ht benzyl' Served, nor are there harmful ff t up to the Emit of ideneacetone brighttrn deposits were formed under other- Solubility wise identical conditions.

,Pyrocatechol which is a krgwn antioxidant in acid tin E l 3 plating solutions, has a bene cial eifect W en emp oyed in the tin plating solutions of the invention in small Platmg bath was Prepared from the feuewmg meamonnts. tenals:

The temperature of the plating solution is preferably Grams/m6 held below C. for best stability, but the maintenance 35 stannous Sulfate of a specific operating temperature in the tin electrolytes cresolsflfcmc aeld 260 is not critical for the production ofbright coatings. Fermalm "1 2 The following examples are further illustrative of the Ether 9 Polyg yeol "'1' present invention, and it will be understood that the in- Benzyhdeneaeetone vention is not limited thereto: 40 Bright deposits were obtained at 20' to 30 C. over a current density range from 1 to 4 amps. per sq. decimeter; Example 1 The ether of polyglycol employed as a nonionic wetting Eight plating solutions'were prepared from stannous agent was thg Same as Example sulfate, sulfuric acid, formalin (aqueous formaldehyde solution of approximately 37% HCHO content), a poly- Example 4 v ethyleneglycol wetting agent, and an olefinic brightener A tin plating solution that gave a very bright tin elecas indicated in Table I. The preferred temperature and trodeposit at 15 to 30 C. when operated at 1 to 3.5 cathode current density ranges in which smooth, bright amps/sq. decimeter has the following composition: tin plates were electrodeposited from the several acid plat- Grarns/ liter 1 ing solutions are also listed in the table. Tin as fluoborate 40 The wetting agents employed were ether of polyethoxy- Fluoboric acid 80 ethanols which contained approximately 11 C H O radi- Wetting agent 2 cals in solutions 1H, IV, and VI, approximately 15 C H O Pyridy-lideneacetone 0.3 radicals in solutionsV, VII, and VIII, 25 C H O radicals Formalin 1 in solution II, and 30 C H4O radicals in solution I. Pyrocatechol 1.5

TABLE I Plating Solution No. Composition, grams/liter I II III IV V VI VII VIII stannous sulfate 60 80 60 7O 60 80 Sulfuric acid .100 so 80 120 100 Formalin- 1 1.5 0.8 1.6 0.8 5 0.8 1 Wetting agen 1 2 6 5 6 6 6 4 Brightener 1 1 0. 35 0. 65 1.3 0.35 0. 32 0.4 Temperature, 0 20-30 20-30 15-30 20-30 18-30 18-30 20-30 15-30 Current density, amps./sq. decimeter 12.5 12.5 0.8-4 12.5 0.7-3.5 0.7-3.5 12.5 13.5

fi g gige elght bnghteners were used m these Less bright, but still very smooth deposits were obtamed when the pyrocatechol was omitted from the bath (1) Styrene composition. The ether of polyglycol was the same as in (H) Cinnamyl alcohol 75 Example 2.

Example 5 A bright tin plating solution was prepared from the following materials:

Grams/liter Tin as divalent sulfate 35 Sulfuric acid 150 Wetting agent 6 Formalin 1 Benzylideneacetone 0.3 Pyrocatechol 0.8

At a bath temperature of 20 to 35 C., the bright cathode current density range extended from 1 to 4 amps/sq. decimeter. The wetting agent employed was a ether of polyethyleneglycol containing approximately 15 C2H4O radicals per molecule. Omission of the pyrocatechol from the bath resulted in smooth, but less bright deposits.

Example 6 TABLE II Plating Solution No. Composition, grams/liter IX X XI XII Tin (as sulfate) 30 40 35 35 Sulfuric acid (free) 100 130 100 150 Wetting agent 6 7 6 6 Formalln 1. 5 0.8 PyrocatechoL 0. 8 Brightener A 0.25 0. 4 2 0. 3 Brightener B"..- 0. 05 0. 6 1. 1. 0 Temperature, C 20-30 18-30 20-30 20-35 Current density amps. per sq. decimeter 1-4 0. 8-3. l-4 1-4 The wetting agents in solutions IX to XH had approximately 1015, 30, 25, C H O radicals per molecule respectively. The olefinic brighteners A were benzylideneacetone (IX and XII), furfurylideneacetone (X), and 2- furylacrylic acid (XI). The imidazolidine derivatives employed as brighteners B may be prepared by the method of US. Patents 2,528,378, 2,773,068 and 2,781,354, and were of the formula A substantial broadening of the bright plating range was achieved by the addition of the imidazoline derivatives as compared to otherwise identical solutions not containing an imidazoline derivative. This effect was noticeable not only in the range of fully bright deposits, but also in the semi-bright range. The use of formaldehyde is not absolutely necessary when imidazoline derivatives are employed as secondary brighteners.

Example 7 The imidazolidine derivatives of the invention are equally elfective as secondary brighteners in tin plating solutions which contain sulfuric, fiuoboric, and aromatic sulfonic acids as conductivity increasing and ionization repressing agents. Fully bright tin electrodeposits were obtained from a solution of the following composition under the operating conditions indicated:

brightener B was-an imidazoline derivative of the formula shown in Example 6 in which R was C H R was CH -COONa, R was sodium. Omission of brightener B from the composition reduced the bright plating range, and particularly the semi-bright plating range.

Example 8 A stock solution was prepared to the following composition:

Grams/liter Tin (as stannous sulfate) 30 Free sulfuric acid Ether of polyglycol (abt. 15 C H O groups) 6 Benzylideneacetone 0.26

Three batches of this solution were mixed with the following secondary brighteners respectively:

Grams/liter (a) Formalin 1.5 (b) Imidazoline derivative 0.5 Formalin 0.8

(c) Imidazoline derivative 1.0

The imidazoline derivative employed was the same as in Example 6, D(. The three plating solutions were used at temperatures between 20 and 30 C. and gave at least semi-bright, smooth deposits at cathode current densities from 0.5 to 4 amps. per square decimeter (about 4.5 to 36 amps/sq. ft.). The fully bright range, however, was broadened significantly as the formalin of batch (a) was gradually replaced by the imidazoline derivative.

While the invention has been described with particular reference to specific embodiments it is to be understood that it is not limited thereto but is to be construed broadly and restricted solely by the scope of the appended claims.

What we claim is:

1. An aqueous acid bright tin electroplating solution including a tin salt, free acid, and as a primary brightener, an effective amount of a compound of the formula XCH=CHY, wherein X is phenyl, furfuryl, or pyridyl, and Y is a member of the group consisting of hydrogen, formyl, carboxyl, alkyl, hydroxyalkyl, formylalkyl, and acyl radicals of carboxylic acids, said compound being dissolved in said aqueous plating solution.

2. A solution as set forth in claim 1, further including, as a secondary brightener, an effective amount of at least one member of the group consisting of formaldehyde and imidazoline derivatives of the formula wherein R is an alkyl radical having at least five carbon atoms, R is a member of the group consisting of hydrogen and CH -COOH, and R is a member of the group consisting of hydrogen and monovalent metal, said secondary brightener being dissolved in said solution.

3. A solution as set forth in claim 2, further including a Wetting agent.

4. A solution as set forth in claim 3, wherein said wetting agent is nonionic.

5. A solution as set forth in claim 3, wherein said wetting agent is a water-soluble ether of polyglycol.

6. A solution as set forth in claim 3, wherein X is phenyl.

7. A solution as set forth in claim 3, methoxyphenyl.

8. A solution as set forth in claim 3, furfuryl.

9. A solution as set forth in claim 3, pyridyl.

10. A solution as set forth in claim 3, the acyl radical of a carboxylic acid.

11. A solution as set forth in claim 5, sulfophenyl.

12. A solution as set forth in claim 5, further including pyrocatechol as an antioxidant.

13. A method of electrodepositing bright tin on an article which comprises making said article the cathode in an aqueous solution including a soluble tin salt, free acid, a nonionic wetting agent, and eifective amounts of primary and secondary brighteners, said primary brightener being a compound of the formula X--CH CHY, wherein X is phenyl, furfuryl, or pyridyl, and Y is a member of the group consisting of hydrogen, formyl, carboxyl, alkyl, hydroxyalkyl, formylalkyl, and acyl radicals of carboxylic acids, said compound being dissolved in said aqueous plating solution, and said secondary brightener including at least one member of the group wherein X is wherein X is wherein X is wherein Y is wherein X is 8 consisting of formaldehyde and imidazoline derivatives'of the formula wherein R is an'alkyl radical having at least five carbon atoms, R is a' member of the group consisting of hydrogen and CH COOH, and R is a member of the group consisting of hydrogen and monovalent metal, said secondary brightener being dissolved in said solution.

14. A method as set forth in claim 13, wherein said wetting agent is a water soluble ether of polyglycol.

15. A method as set forth in claim 13, wherein said free acid is selected from the group consisting of sulfuric acid, fluoboric acid, and phenolsulfonic acids.

16. A method as set forth in claim 13, wherein said solution is at a temperature not substantially higher than 35 C.

References Cited UNITED STATES PATENTS ROBERT K. MIHALEK, Primary Examiner.

JOHN H. MACK, Examiner.

G. KAPLAN, Assistant Examiner. 

